Neutrino Masses and the Dark Energy Equation of State:Relaxing the Cosmological Neutrino Mass Bound

At present, cosmology provides the nominally strongest constraint on the masses of standard model neutrinos. However, this constraint is extremely dependent on the nature of the dark energy component of the Universe. When the dark energy equation of state parameter is taken as a free (but constant) parameter, the neutrino mass bound is $\sum _{}^{}{m}_{\nu }\le 1.48\mathrm{eV}$ (95% C.L.), compared with $\sum _{}^{}{m}_{\nu }\le 0.65\mathrm{eV}$ (95% C.L.) in the standard model where the dark energy is in the form of a cosmological constant. This has important consequences for future experiments aimed at the direct measurement of neutrino masses. We also discuss prospects for future cosmological measurements of neutrino masses.